The Phono Stage

[quan]

Hi guys , just completed my phonostage-measured DC offset at 15/20mV-?any problem?

 

[JBdV]

Hello Peter, can you give some information about signal to noise ratio? Did you measure this ?

 

[Peter Daniel]

I didn't measure it, but subjectively it's very quiet. You may check this review of the original circuit (I use different parts and completely different PS): H A L L O F F A M E

Hi guys , just completed my phonostage-measured DC offset at 15/20mV-?any problem?

It shouldn't be a problem if your amp does not amplify DC. The simplified GC does, and coupling cap might be needed with such offset values.

The offset will depend on a particular OPA637 chip; some chips will produce much less offset.

 

[quan]

Sorry Peter, NOOB-GC?-what output coupling cap will be needed?

 

[Peter Daniel]

Check the offset with the amp connected for different volume settings (speaker disconnected when testing). If it exceeds 100mV use 2.2 - 4.7uF coupling caps.

 

[quan]

Hi Peter, plugged in it today-the transformer humming and vibrating like crazy and feel as though not enough gain( compare with herron audio phonostage-66db)
The tranny was dropped onto the floor the other day!!! Likely to be faulty.
Please advise how to wire with dual secondaries toroidal transformer. NOOB question.
Thanks.

 

[Peter Daniel]

I'm using 2 x 12V transformer, which unloaded produce approx 14V AC per secondary.

In attached pic, you can see 4 pads (on a left). Those pads are for external transformer connection: first two from the top are for one secondary, the other two for the other secondary. You will need approx 19V after rectification and 15V regulated. If you can get 15V because of too low voltage on secondaries, settle for lower regulated voltage, it will not affect anything (adjust with changing R7 and R8)

 

[quan]

Hi peter, do the secondaries need to be in phase?

 

[Peter Daniel]

As both positive and negative regulator circuits are completely independent, the secondaries do not need to be in phase; you can also use two separate transformers with single secondaries.

 

[quan]

Thanks Peter.

 

[Algar_emi]

Here my own compilation of the complete parts list phono preamp and shunt regulator section with distributors, prices, etc...Maybe Peter can comment on its latest findings about the circuit to see if this list is still up to date. I included the omission of R7, output resistor of the preamp section.

 

[Algar_emi]

Here my own compilation of the complete parts list phono preamp and shunt regulator section with distributors, prices, etc...Maybe Peter can comment on its latest findings about the circuit to see if this list is still up to date. I included the omission of R7, output resistor of the preamp section.

 

[Algar_emi]

Here an updated version, removed C3-C6 on the Shunt regulator as suggested by Peter.

 

[Peter Daniel]

In majority cases C4 is still needed as most LM337 types will not produce correct voltage without it: http://www.diyaudio.com/forums/audio-sector/151938-phono-stage-8.html#post2000870

 

[Peter Daniel]

Also, while you specify Nichicon (Mouser 647-UES1H100MPM) for C3, the Wima MKS2 may be actually a better choice (when BG N is not available)

 

[chrismercurio]

Peter,

Do you have a high gain version of this available? I'm not sure if it is just a few parts in the BOM that need to change or if it is entirely different.

Thanks,

 

[Peter Daniel]

I was told that the gain can be adjusted with R2, R3 (3k3 presently) and of course by using cartridge with different internal resistance.

 

[Algar_emi]

Thanks Peter for the precision. SB

 

[chrismercurio]

Peter,

A couple of questions:

1. What value is necessary for R2/3 to raise the gain to 90db?

2. IF using a battery supply, is it possible to eliminate caps C4/5? I couldn't find them in the schematic posted on the first page of the thread either.

Best,

Chris

 

[Peter Daniel]

1) I really don't know, never experimented with gain.

2) It could be possible, but again, it needs to be tested. Even with batteries, I usually prefer to use some caps, but much smaller in value.